Circulating hot water system and or appliance

ABSTRACT

A water heating system having a system inlet pipe ( 1.002 ), a hot water delivery pipe ( 1.003 ) and a hot water return pipe ( 1.006 ) connected to a building hot water distribution network ( 1.024 ); the water heating system including one or more water heaters ( 1.001 ), the or each water heater having a heater inlet ( 1.022 ) and a heater outlet ( 1.023 ), a hot water return pipe ( 1.006 ) connected between the system inlet and delivery outlet via the building hot water distribution network to form a close loop hot water supply-return circuit; a pump (1.005) connected to circulate water through the hot water supply-return circuit whereby the pump can circulate water through one or more of the water heaters; a valve means ( 1.007 ) a first non-return valve adapted to prevent inlet water (water delivered to the system inlet) from flowing into the hot water return pipe or the building hot water distribution network.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 13/804,379, filed Mar. 14, 2013, the entiredisclosure of which is hereby incorporated by reference herein, whichclaims priority to Australian patent application number 2012901168,filed Mar. 22, 2012.

FIELD OF THE INVENTION

This invention relates to hot water systems and appliances. They will bedescribed in the context of a circulating hot water system including oneor more instantaneous water heaters.

In particular, the invention can be used in commercial buildings whichhave a high demand for hot water for heating or for use in bathrooms,etc.

BACKGROUND OF THE INVENTION

FIG. 1 shows a circulating water heating system 1.000, which iscontained within an appliance 1.100 schematically represented by a dashand two dot surrounding line. The system has one or more water heaters1.001 a . . . 1.001 n, each having a heater inlet 1.022 and a heateroutlet 1.023. The water heaters can be instantaneous water heaters,which heat the water only when water is drawn off by the users of thesystem. Each heater inlet 1.022 is connected to a system inlet pipe1.002. The system inlet pipe 1.002 is connected to mains water supply orpreheated water source 1.0022 via an appliance inlet fitting at 1.0021,and via which water to be heated is fed into the system. Each heateroutlet 1.023 is connected to a hot water delivery pipe 1.003 which isconnected to a hot water outlet fitting 1.0031 on the outside of theappliance 1.100. The hot water delivery pipe 1.003 is thus connected viafitting 1.0031 and a building hot water distribution network 1.024, to anumber of user outlets or heat exchanger devices 1.004 via, to permitusers to draw off hot water. Each water heater can have an adjustableand or controllable water control valve to control flow of water throughthe water heater. Each water heater can have a flow sensor which canoperate the associated water heater when flow is detected.

The water heaters 1.001 a . . . 1.001 n can have a controllable gasvalve and ignition means. The ignition means can be any suitableignition means such as a pilot flame. The ignition means can be acontrollable ignition means such as a spark generator.

The water heaters are connected in parallel between the system inletpipe 1.002 and the hot water delivery pipe 1.003.

A closed loop hot water supply-return circuit forms a closed circuitwith the hot water delivery pipe 1.003, the building hot waterdistribution network 1.024, which connects back to the appliance 1.100via a hot water return inlet fitting at 1.0061, which in turn connectsto a hot water return pipe 1.006 then system inlet pipe 1.002 and waterheaters 1.001 a . . . 1.001 n. A pump 1.005 is adapted to circulatewater through the water heaters 1.001 a . . . 1.001 n, the hot waterdelivery pipe 1.003, building hot water distribution network 1.024 andthe hot water return pipe 1.006. The hot water return pipe 1.006connects to the system inlet pipe 1.002 so the pump can increase thepressure at the heater inlets 1.022.

A non-return valve 1.007 inhibits reverse flow through the hot waterreturn pipe 1.006, so cold water from main water supply cannot bypassthe water heaters and reach the user outlets 1.004 via the hot waterreturn pipe 1.006 and the building hot water distribution network 1.024.

The pump can be used to circulate water through the water heaters 1.001a . . . 1.001 n to maintain the temperature of the water in the closeloop hot water supply-return circuit above a first thresholdtemperature, so that, when user outlets or heat exchanger devices 1.004are activated, such as by opening a hot water tap, the water will be ata required temperature.

A single water heater can adequately heat a first level of consumption,while two water heaters are required to meet a demand which exceeds thecapacity of a single water heater, and so on. The capacity of each waterheater is a known design factor.

Each water heater can have its own flow sensor although a single flowsensor can be used in the hot water delivery pipe 1.003 or in the systeminlet pipe 1.002.

Each water heater can have a maximum input capacity or flow rating. Thewater heater is designed to heat water at a flow rate up to the maximumflow rate to a specified temperature rise. If the flow through the waterheater exceeds this input capacity, the water heater cannot heat thewater to the required temperature. The water heater can also be designedto have a greater the pressure drop across the water heater when theflow exceeds the maximum flow rate. As the water heaters are inparallel, then, assuming “n” water heaters of the same design, themaximum flow rate for the combination of water heaters to heat water tothe required temperature will be n times the flow rate of a single waterheater.

The pump can be run continuously, or run according to a timer setting,and one of the water heaters or all water heaters are maintainedoperational, so that the pump can circulate hot water through the hotwater delivery pipe 1.003, the building hot water distribution network1.024 and hot water return pipe 1.006, to ensure that hot water isimmediately available at the user outlets 1.004, such as shower taps.

In order to avoid the delivery of water at a temperature below thespecified temperature, flow control means can be used to limit the flowof water through the water heaters to a predetermined maximum flow.While this may avoid the problem of delivering water at a lower thanspecified temperature, it results in a drop in the pressure of the hotwater delivered to the user outlets or heat exchanger devices 1.004.

The present invention proposes an arrangement to mitigate the effects ofdecreased hot water pressure at high flow rates.

SUMMARY OF THE INVENTION

The present invention provides a water heating system having a systeminlet, a delivery outlet and hot water return inlet connected to abuilding hot water distribution network; the water heating systemincluding one or more water heaters, the or each water heater having aheater inlet and a heater outlet, a supplemental path connecting thesystem inlet to the delivery outlet; the supplemental path including aflow control device adapted to permit flow from the system inlet to thedelivery outlet when the pressure at the delivery outlet is lower thanthe pressure at the system inlet by a predetermined pressuredifferential.

The present invention also provides a water heating system having asystem inlet, a delivery outlet and hot water return inlet connected toa building hot water distribution network; the water heating systemincluding one or more water heaters, the or each water heater having aheater inlet and a heater outlet, a supplemental path connecting thesystem inlet to the delivery outlet; the supplemental path bridging thewater heater or water heaters and including a flow control deviceadapted to permit flow from the system inlet to the delivery outlet whenthe pressure differential across the water heater or water heatersexceeds a predetermined pressure differential.

The predetermined pressure differential can correspond to apredetermined water flow rate through the water heaters.

The water heating system can include a hot water return inlet connectingthe remote end of the building hot water distribution network back tothe system inlet of the water heating system whereby its forms acirculation path including the water heaters.

The water heating system can include one or more water heaters, theinlet of each water heater being connected to the system inlet, and theoutlet of each water heater being connected to the delivery outlet.

The water heating system can include a valve means adapted to preventwater delivered to the system inlet from flowing directly into the hotwater return path and building hot water distribution network.

The building hot water distribution network can include one or more useroutlets.

The water heating system can include a supplemental path connecting thesystem inlet to the delivery outlet, the supplemental path including aflow control device such as an electronically controlled valve orpressure activated device oriented so a pressure differential betweenthe inlet of the pressure activated device and the outlet of thepressure activated device enables water at system inlet to be fed to thedelivery outlet when the pressure at the delivery outlet is less thanthat of the system inlet by the operating pressure of the pressureactivated device.

The water heating system can include a storage tank between the systeminlet and the pressure activated device, whereby water from the storagetank is delivered to the delivery outlet when the pressure differentialacross the pressure activated device opens the pressure activateddevice.

The pump can be connected to the inlet of the storage tank, the waterheating system including a recirculation pipe (3.016) and a secondnon-return valve (3.015) connecting the outlet of the storage tank tothe system inlet.

The water heating system can include a third non-return valve connectedbetween the system inlet and the pump outlet to prevent delivery ofwater from the pump to the system inlet without passing through thestorage tank.

The invention also provides a method of operating a water heating systemincluding: one or more water heaters having their heater inletsconnected in parallel to a system inlet pipe and their outlets connectedin parallel to a hot water delivery pipe; these water heaters connectedin parallel to the system inlet pipe and the hot water delivery pipe canbe in cascade or in equal differential pressure arrangement; a hot waterreturn pipe connecting the end of the building hot water distributionpipe to the system inlet pipe; a circulating pump adapted to circulatewater through the hot water delivery pipe and the building hot waterdistribution pipe and the hot water return pipe and the system inletpipe and one or more selected ones of the water heaters; a supplementalflow pipe connected from the system inlet pipe to the hot water deliverypipe, the supplemental flow pipe including a pressure activated device;the method including the steps of: sensing the pressure differentialacross the water heaters; opening the pressure activated device when thepressure differential exceeds a predetermined value.

The present invention provides a system which can be purpose built orembodied within an appliance.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment or embodiments of the present invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic illustration of a multi-water heater circulatingwater heating system.

FIG. 2 is a schematic illustration of a circulating water heating systemaccording to an embodiment of the invention.

FIG. 3 is a schematic illustration of a water heating system accordingto a further embodiment of the invention.

FIG. 4 shows a modification of the embodiment of FIG. 2.

FIG. 5 is a flow diagram illustrating an operating mode of a systemaccording to an embodiment of the invention.

FIG. 6 illustrates a perspective view of a water heating appliance whichhas one of the embodiments of the invention illustrated in FIGS. 2 to 5.

The numbering convention used in the drawings is that the digits infront of the full stop indicate the drawing number, and the digits afterthe full stop are the element reference numbers. Where possible, thesame element reference number is used in different drawings to indicatecorresponding elements.

The drawings are intended to illustrate the inventive features of theembodiments illustrated and are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENT

The invention will be described with reference to the embodimentsillustrated in the accompanying drawings.

FIG. 2 illustrates a system 2.000 according to a first embodiment of theinvention. The system of FIG. 2 is similar to that of FIG. 1, butincludes additional elements to mitigate at least one of the problems ofexisting circulating hot water systems.

The system 2.000 includes a bank of instantaneous water heaters orcontinuous flow water heaters 2.001 a to 2.001 n with system inlet pipe2.002 connected to mains water supply or pre-heated water source, a hotwater delivery pipe 2.003 connected to building hot water distributionnetwork 2.024 with one or more hot water consumption outlets 2.004, ahot water return pipe 2.006 connected to the remote end of the buildinghot water distribution network 2.024 to form a close circuit, pump2.005, non-return valve 2.007, temperature sensor 2.008, a supplementalflow pipe 2.011 with a pressure activated device 2.012 forming asupplemental path between the system inlet pipe 2.002 and the hot waterdelivery pipe 2.003. The pump outlet also connects with the system inletpipe 2.002 via non-return valve 2.007. A controller 2.010 can also beincluded. The controller 2.010 can be responsive to sensors such astemperature sensors, including temperature sensor 2.008, or pressuresensors, or both, to control one or more of the devices of the waterheating system. The controller 2.010 can control the pump. Thecontroller 2.010 can control the water flow in the water heaters. Thecontroller 2.010 can control the heating operation of the water heaters.However, the water heaters may alternatively be automatically responsiveto the flow of water to heat the water.

The pressure activated device 2.012 is included in the supplemental flowpipe 2.011. The pressure activated device 2.012 permits flow from itsinlet to its outlet when the pressure at the outlet of the pressureactivated device 2.012 is less than the pressure at the inlet of thepressure activated device by ΔP, where ΔP is the operating pressuredifferential of the pressure activated device. Flow in the oppositedirection is always blocked by pressure activated device 2.012.

The supplemental flow pipe 2.011 is connected between the system inletpipe 2.002 and the hot water delivery pipe 2.003 and provides asupplemental path when the water pressure at the inlet side of pressureactivated device 2.012 exceeds the pressure in the hot water deliverypipe 2.003 adjacent the outlet of the pressure activated device 2.012 byan amount determined by the operating characteristics of valve 2.012,ie, when the pressure on the downstream side of the pressure activateddevice 2.012 is reduced to a point at which the pressure differentialexceeds the pressure setting of the pressure activated device. Thepressure differential at this operating point is determined by the mainswater supply pressure at system inlet and the pressure drop through thesystem inlet pipe 2.002, the water heaters and hot water delivery pipe2.003 due to flow. This arrangement enables the pressure at the deliveryoutlet to be maintained at a sufficient level when heavy demand (flow)occurs, trading off temperature for pressure by allowing unheated waterto enter the hot water delivery pipe 2.003 when extreme demand occurs.The double headed arrow between the one way valve 2.007 and the systeminlet pipe 2.002 indicates that the flow can be reversed when very highdemand occurs and causes a pressure drop across the water heaters ofsufficient magnitude to activate the pressure activated device 2.012.

Each water heater can be equipped with monitor means to monitor thewater heater for faults. Additional control means, such as controller2.010 can be used to respond to fault signals from the water heatermonitor means. The controller 2.010 can also activate an alarm inresponse to a fault indication. The controller 2.010 can be combinedwith a second controller, for example in a programmable controller, orit can be incorporated in a centralized building monitoring system.

While the pump can be run continuously, in an alternative mode ofoperation, the pump may be run intermittently. During periods of low orzero use, the water in the close loop hot water supply-return circuitwill cool. When the temperature sensor 2.008 detects a temperature belowthe predetermined first threshold, it activates the pump 2.005. The pumpthen circulates the water in the hot water delivery pipe 2.003, thebuilding hot water distribution network 2.024 and hot water return pipe2.006 through the water heaters. When the temperature sensor 2.008detects that the temperature of the water from the pump exceeds a secondthreshold temperature higher than the first threshold temperature, thecontroller 2.010 turns the pump off. Thus the temperature of the waterin the close loop hot water supply-return circuit can be maintainedwithin a desired temperature range without the need to maintaincontinuous pump operation.

During periods of hot water consumption, the controller 2.010 controlsthe water control valves of the water heaters so water is allowed toflow through only the required number of water heaters, the number ofwater heaters used depending on the designed pump flow rate and the flowdemand.

The system of FIG. 2 can be purpose built or incorporated in anappliance 6.100 as illustrated in FIG. 6, where a mains water supply orpre-heated hot water inlet 6.0021, a hot water outlet 6.0031 and a HWreturn inlet 6.0061 are provided. The appliance 6.100 has four modularwater heaters 6.001 a, 6.001 b, 6.001 c and 6.001 d and can be a standalone floor mounted system or a wall mounted system.

FIG. 3 illustrates a system according to a further embodiment of theinvention. This arrangement is adapted to compensate for the loss oftemperature at the hot water delivery pipe 2.003 of FIG. 2 when thesupplemental flow pipe 2.011 is used.

This embodiment adds a storage tank 3.013 in the supplemental flow pipe3.011, and a recirculation pipe 3.016 with non-return valve 3.015, aswell as a further non-return valve 3.014, to the arrangement of FIG. 2.In addition, the temperature sensor 3.008 is located to respond to thetemperature of water from the storage tank 3.013.

The non-return valves 3.007, 3.014, & 3.015 are arranged to direct theflow of water to permit the water heating system to deliver heated waterfrom the water heaters 3.001 a . . . 3.001 n and from the storage tank3.013 simultaneously to the hot water delivery pipe 3.003 during heavydemand, and to permit the pump to circulate water from the hot waterdelivery pipe 3.003, via the building hot water distribution pipe, tothe hot water return pipe 3.006, the storage tank 3.013 and through thewater heaters 3.001 a . . . 3.001 n, so the heated water in the storagetank 3.013 can be replenished. Thus non-return valve 3.007, blocksreverse flow into the hot water return pipe 3.006 from mains watersupply at system inlet while permitting the pump to circulate waterthrough storage tank 3.013.

Non-return valve 3.014 enables water from the mains water supply atsystem inlet to enter the storage tank 3.013 when the pressure activateddevice 3.012 is open. Non-return valve 3.015 inhibits water from systeminlet from short-circuiting the storage tank 3.013 and being supplieddirectly to the pressure activated device 3.012.

The storage tank 3.013 is well insulated. Thus it will retain itstemperature above the lower temperature threshold for a longer periodthan the hot water delivery pipe 3.003 and the building hot waterdistribution pipe 3.024, which have a larger surface area to watervolume ratio than the storage tank 3.013. Hence, even if the efficiencyof the insulation, if any, on the hot water delivery pipe 3.003 and thebuilding hot water distribution pipe 3.024 were to be equivalent to thatof the storage tank 3.013, the temperature of the water in the storagetank would fall at a slower rate than the temperature of the water inthe hot water delivery pipe 3.003 and the building hot waterdistribution pipe 3.024.

The pressure differential across pressure activated device 3.012 isdetermined by the flow of water through the water heaters in the waterheating system. High demand for water in the hot water delivery pipe3.003 increases the pressure differential across pressure activateddevice 3.012. When the pump 3.005 is idle, and the inlet water pressureat system inlet pipe 3.002 exceeds the water pressure in the hot waterdelivery pipe 3.003 by the pre-set operating pressure differential ofthe pressure activated device 3.012, some water flows from the mainswater supply through non-return valve 3.014, storage tank 3.013 andpressure activated device 3.012, then join with hot water delivered fromthe water heaters. The non-return valve 3.015 in the recirculation pipe3.016 inhibits flow from mains water supply via the recirculation pipe3.016.

A flow detector 3.018 or flow detector in each water heater can detectthe flow rate and the controller 3.010 can select the appropriate numberof water heaters to heat the required flow of water.

The system has a number of operating modes.

A first operating mode is the maintenance of water temperature in theclose loop hot water supply-return circuit when there is no water drawnby the users.

A second mode of operation is the supply of hot water and maintenance ofthe water temperature in the hot water supply-return circuit when thewater is drawn at a flow less than the maximum design flow of the waterheaters.

A third mode of operation is the supply of hot water and maintenance ofwater temperature in the hot water supply-return circuit when the flowexceeds the maximum design flow of the water heaters.

A fourth mode of operation occurs when water is drawn while the pump isoff and the flow of water is less than the maximum design flow of thewater heaters.

A fifth mode occurs while the pump is off and the flow exceeds themaximum design flow of the water heaters.

In the first operating mode, the water heating system maintains thetemperature of the water in the close loop hot water supply-returncircuit when there is no water drawn off by the user outlets or heatexchanger devices 3.004.

Pump 3.005 is connected to the inlet of storage tank 3.013. Thetemperature sensor 3.008, which is located on the outlet side of thestorage tank 3.013, detects the temperature at the outlet of the storagetank 3.013. When the temperature sensed by the temperature sensor 3.008detects that the temperature has fallen below a first temperaturethreshold, it turns the pump 3.005 on. This causes the water in the tankto be circulated around a water circuit including recirculation pipe3.016, non-return valve 3.015, system inlet pipe 3.002, through aselected one of the water heaters 3.001 a . . . 3.001 n, into the hotwater delivery pipe 3.003, the building hot water distribution pipe, thereturn pipe 3.006, the pump 3.005, non-return valve 3.007, and into theinlet of storage tank 3.013. The temperate sensor 3.008 and itsassociated control system, can allow users to define a minimum run timefor the pump 3.005 so that it can avoid short-cycling of the pump. Thewater is circulated around this path until the temperature sensed by thetemperature sensor 3.008 is above a second temperature threshold higherthan the first temperature threshold. The pump and water heaters canthen be turned off until the temperature sensor again detects atemperature below the first temperature threshold. Hence the water inthe storage tank can be maintained at a temperature within a desiredtemperature range while there is no water being drawn off.

A person skilled in the art will understand that, in this first mode,the pressure from the pump 3.005 while the pump is operating preventsflow from non return valve 3.015 through non return valve 3.014 due topressure drops through the storage tank 3.013 and non return valve3.015.

In the second mode of operation when the water is drawn at a flow lessthan the maximum design flow of the water heaters with the pump isrunning, in this case, the temperature sensor 3.008 detects the watertemperature is below the first threshold temperature and the controller3.010 turns the pump on. So long as the pressure delivered by the pump3.005 can overcome the pressure loss at the storage tank, non returnvalve 3.015 and friction loss of the water circuit, water flows from thebuilding hot water distribution pipe 3.024 into hot water return pipe3.006, via the pump 3.005, non-return valve 3.007, into the storage tank3.013, via recirculation pipe 3.016, non-return valve 3.015, joins withthe mains water supply drawn into the system as demanded by user outlets3.004, and the water heaters. Water pumps through the water circuit willbe reheated by the water heaters 3.001 a . . . 3.001 n until watertemperature sensed by temperature sensor 3.008 reaches the secondthreshold temperature and turns the pump off. Thus, water temperature inwater circuit and storage tank can be maintained.

In the case where the demand flow exceeds the maximum design flow forthe water heaters while the pump is operating (third mode of operation),the operation changes as additional flow from the water heating systemis required to meet the flow demand. When the pressure at the outlet ofpump 3.005 drops below the system inlet pressure at 3.002, the nonreturn valve 3.015 has higher pressure at its outlet than its inlet, andflow through this valve ceases. At the same time non return valve 3.014has higher pressure at its inlet than its outlet, so water from themains water supply can flow through non return valve 3.014, storage tank3.013 displaying hot water out of the storage tank, via pressureactivated valve 3.012 and join with the hot water delivered by the waterheaters from the hot water delivery pipe 3.003. Thus water temperaturedelivered by the water heating system can be maintained and avoidexcessive pressure loss due to high demand. (Note: there will be noblending as non return valve 3.007 is closed, no flow from the pump).

In first, second and forth modes operations, the pressure activateddevice 3.012 does not permit flow from the outlet of storage tank 3.013to the hot water delivery pipe 3.003 because the pressure drop throughthe heater is not sufficient to operate the pressure activated device3.012.

In the forth mode of operation water is drawn at a flow less than themaximum design flow of the water heaters. In this instance, again thepressure activated device 3.012 remains closed, as the flow is below themaximum design flow of the water heaters. The pump 3.005 can be turnedoff, when temperature sensor 3.008 detects that the water temperaturehas reached the second temperature threshold and it is above the firsttemperature threshold. Water flow drawn from hot water consumptionoutlet 3.0041 . . . 3.004M will activate one or more of the waterheaters determined by controller 3.010.

However, if the demand is prolonged, the temperature of the water in thestorage tank may fall below the first temperature threshold. In thiscase, the temperature sensor 3.008 will turn the pump on to maintain thewater in the hot water supply-return circuit and the storage tank 3.013within the required temperature range. Thus, the water in the storagetank will be delivered to the system inlet pipe 3.002 and circulatedaround the water circuit to raise the temperature of the water in thehot water supply-return circuit and the storage tank to the secondthreshold temperature. At this stage, the temperature sensor 3.008 willturn pump 3.005 off.

This also has the effect of ensuring that, if the water is being drawnoff from a tap 3.0041, which is upstream of one or more other taps(3.004M), nearer to the heaters, the water in the building hot waterdistribution pipe is maintained at the required temperature.

In the third and fifth modes of operation, the flow of water drawn offexceeds the maximum designed flow of the water heaters. In this case,the pressure drop across pressure activated device 3.012 will besufficient to permit flow from the storage tank outlet through thepressure activated device into the hot water delivery pipe 3.003, due tothe pressure drop through the water heaters. The non-return valves 3.007and 3.015 prevent water from mains water supply from flowing in theirrespective pipes. Thus water will flow from mains water supply, throughnon-return valve 3.014, through storage tank 3.013, and into pressureactivated device 3.012 to hot water delivery pipe 3.003. Thus, thestored heated water from storage tank 3.013 will be delivered to the hotwater delivery pipe 3.003. Thus this system can mitigate both the dropin pressure and the drop in temperature when the flow through the waterheaters reaches the maximum designed flow.

When there is low demand on the hot water consumption outlets, thetemperature sensor 3.008 and its associated control system, will detectwhen the temperature in the pipe connected to the outlet of the storagetank 3.013 falls below the first threshold temperature and will turn thepump on. The non-return valve 3.014 inhibits water from the pump fromflowing directly to the mains water supply or system inlet pipe 3.002,and the pump thus causes water in the storage tank 3.013 to becirculated around the hot water supply-return circuit, via thenon-return valve 3.015 and the water heaters 3.001 a . . . 3.001 n tothe hot water delivery pipe 3.003.

The pump 3.005 remains off until the temperature sensor 3.008 detectsthat the water from storage tank 3.013 has fallen below the firsttemperature threshold.

The operating pressure of the pressure activated device determines theflow paths during different operating conditions. In particular, thepressure activated device permits mains water to flow through thestorage tank when there is high demand, compensating for pressure lossesin the water heaters with additional heated water from the storage tank3.013. This mitigates the pressure/temperature compromise of thearrangement of FIG. 2.

When there is low demand, the pressure activated device inhibits flowfrom the mains water supply through the storage tank. When thetemperature sensor 3.008 and its associated control system turns thepump on, the water is circulated from the hot water return pipe 3.006,through the storage tank 3.013, along pipe 3.016 via non-return valve3.015, through a selected one of the heaters 3.001 a . . . 3.001 n tothe hot water delivery pipe 3.003 and the building hot waterdistribution pipe 3.024. Thus the water in the hot water delivery pipe3.003, the building hot water distribution pipe 3.024, the hot waterreturn pipe 3.006, and the storage tank 3.013 can be heated by thepumped circulation.

The embodiment of FIG. 3 is incorporated within an appliance 3.100 whichis schematically represented by a dash then two dot broken line in FIG.3, or in an appliance housing 6.100 such as illustrated in FIG. 6.However, if desired, the system can be purpose built.

If desired, as illustrated in FIG. 4, the outlet of the pump 4.005 canalternatively be connected to the hot water delivery pipe 4.003 with thenon-return valve 4.007 being on the inlet side of the pump 4.005. Whileit may not a regular practice to install non-return valve 4.007 at thepump inlet, it will fulfill the function of stopping water flow from themains water supply to any of the hot water consumption outlets 4.004 viathe hot water return pipe 4.006.

FIG. 5 is a flow diagram illustrating a method of operating acirculating water heating system according to an embodiment of theinvention.

The system starts operating at step 5.120. A time delay 5.122 can beprovided to control the rate of repetition of the process.

A check of the flow detector output is carried out at step 5.124, if noflow is detected, the system returns to a no flow temperaturemaintenance routine 5.125. Using the feedback loop from the output offlow detection step 5.124, the maintenance routine 5.125 input isperiodically updated (delay 5.122) from the flow detection process at5.124 indicating whether flow has commenced.

If flow is detected, the level of flow is then analysed at steps 5.126to 5.130. At step 5.126, if the flow is requires all N water heaters ofthe system, then the N water heaters are turned on at step 5.128. If theflow does not require all N water heaters, a series of checks of theflow level are carried out (dashed line) to determine the number ofwater heaters required to accommodate the flow level. The final check isshown at 5.130 to determine if the flow requires 2 water heaters. If so,then the two water heaters selected are turned on at step 5.132.

If the flow requires less than 2 water heaters, a single water heater isselected at 5.134.

A temperature sensor can also be incorporated in the water heatercontrol when the water temperature at the system outlet exceeds apredetermined threshold, e.g., 70° C., water heaters can be turned offone at a time until the temperature is within a predetermined range.

Concurrently, the pressure activated device monitors the pressuredifferential ΔP at step 5.140, and when ΔP exceeds PD, at step 5.142 thepressure activated device opens the supplemental path from the watersupply or system inlet pipe to the hot water delivery pipe. When ΔPfalls below PD, the supplemental path is closed at step 5.144.

Of course, the process can be implemented in other ways. For example,the flow detector output can be compared with a look-up table todetermine which water heaters need to be activated.

The term “non-return valve” is equivalent to “one-way-valve”.

In this specification, reference to a document, disclosure, or otherpublication or use is not an admission that the document, disclosure,publication or use forms part of the common general knowledge of theskilled worker in the field of this invention at the priority date ofthis specification, unless otherwise stated.

In this specification, terms indicating orientation or direction, suchas “up”, “down”, “vertical”, “horizontal”, “left”, “right” “upright”,“transverse” etc. are not intended to be absolute terms unless thecontext requires or indicates otherwise.

Where ever it is used, the word “comprising” is to be understood in its“open” sense, that is, in the sense of “including”, and thus not limitedto its “closed” sense, that is the sense of “consisting only of”. Acorresponding meaning is to be attributed to the corresponding words“comprise”, “comprised” and “comprises” where they appear.

It will be understood that the invention disclosed and defined hereinextends to all alternative combinations of two or more of the individualfeatures mentioned or evident from the text. All of these differentcombinations constitute various alternative aspects of the invention.

While particular embodiments of this invention have been described, itwill be evident to those skilled in the art that the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. The present embodiments and examplesare therefore to be considered in all respects as illustrative and notrestrictive, and all modifications which would be obvious to thoseskilled in the art are therefore intended to be embraced therein.

What is claimed is:
 1. A water heating system connected to a buildinghot water distribution network, said water heating system comprising: asystem water inlet; a water delivery outlet connected to the buildinghot water distribution network; a hot water return inlet connected tothe building hot water distribution network; one or more water heaters,each water heater having a heater inlet that is connected to the systemwater inlet to receive water from a water supply and to the hot waterreturn inlet to receive water from the building hot water distributionnetwork and a heater outlet that is connected to the delivery outlet todeliver water from the water heater to the building hot waterdistribution network; and an unheated supplemental water flow pathconnecting the system water inlet to the delivery outlet, thesupplemental path bridging the water heater or water heaters andincluding a flow control device adapted to permit flow from the systemwater inlet to the delivery outlet through the supplemental path,simultaneously with flow from the system water inlet to the deliveryoutlet through the one or more water heaters, when a pressuredifferential across the water heater or water heaters exceeds apredetermined pressure differential.
 2. A system as claimed in claim 1,wherein the flow control device comprises a pressure activated deviceoriented so a pressure differential between an inlet of the pressureactivated device and an outlet of the pressure activated device enableswater from the system water inlet to be fed to the water delivery outletwhen pressure at the inlet of the pressure adjusted device exceedspressure of the pressure activated device outlet by an operatingpressure of the pressure activated device.
 3. A system as claimed inclaim 2, including a non-return valve in the hot water return inlet. 4.A system as claimed in claim 1, wherein each water heater includes awater control valve.
 5. A system as claimed in claim 1, including a flowdetector detecting a level of flow of water through the system, orincluding a flow detector in each water heater detecting a respectivelevel of flow through each water heater, and a controller responsive tothe flow detector or flow detectors to select a number of heaters to beactivated.
 6. A system as claimed in claim 1, including a firsttemperature sensor sensing a temperature of water delivered to the oneor more water heaters via the hot water return pipe, and a pump in thehot water return inlet being controlled by the first temperature sensor,whereby the pump is turned on when the temperature sensed by thetemperature sensor falls below a first predetermined temperature.
 7. Asystem as claimed in claim 1, wherein said system is incorporated withinan appliance having fittings for connection to a mains supply orpre-heated hot water inlet supply, a hot water outlet and a hot waterreturn inlet.
 8. A method of operating a circulating water heatingsystem including one or more water heaters having respective heaterinlets connected in parallel to a system water inlet and respectiveheater outlets connected in parallel to a hot water delivery outlet, thewater heaters connected in parallel between the system inlet and the hotwater delivery outlet, a hot water return inlet connecting an end of abuilding hot water distribution network to the system water inlet, acirculating pump adapted to circulate water through the hot waterdelivery outlet and the building hot water distribution network and thehot water return inlet and the water heaters, and an unheatedsupplemental water flow path connected from the system water inlet tothe water delivery outlet, the supplemental water flow path including apressure activated device, the method comprising the steps of: sensing apressure differential across the water heaters; and opening the pressureactivated device when the pressure differential exceeds a predeterminedvalue so that water flows through the supplemental path simultaneouslywith flow from the system water inlet to the delivery outlet through theone or more water heaters.
 9. A method as claimed in claim 8, whereinsaid system is incorporated within an appliance having fittings forconnection to a mains or pre-heated hot water supply inlet, a hot wateroutlet and a hot water return inlet.
 10. A system as claimed in claim 1,wherein the supplemental water flow path connects the system water inletand the hot water return inlet to the delivery outlet.
 11. A waterheating system connected to a building hot water distribution network,said water heating system comprising: a system water inlet; a waterdelivery outlet connected to the building hot water distributionnetwork; a hot water return inlet connected to the building hot waterdistribution network; the water heating system including one or morewater heaters, each water heater having a heater inlet that is connectedto the system water inlet to receive water from a water supply and tothe hot water return inlet to receive water from the building hot waterdistribution network and a heater outlet that is connected to thedelivery outlet to deliver water from the water heater to the buildinghot water distribution network; and a supplemental water flow pathconnecting the system water inlet to the delivery outlet, thesupplemental path bridging the water heater or water heaters andincluding a flow control device adapted to permit flow from the systemwater inlet to the delivery outlet through the supplemental path,simultaneously with flow from the system water inlet to the deliveryoutlet through the one or more water heaters, when a pressuredifferential across the water heater or water heaters exceeds apredetermined pressure differential, wherein the supplemental water flowpath is connected to the hot water return inlet to receive water fromthe building hot water distribution network at a point in thesupplemental water flow path between the system water inlet and thedelivery outlet.
 12. A system as claimed in claim 11, wherein the flowcontrol device comprises a pressure activated device oriented so apressure differential between an inlet of the pressure activated deviceand an outlet of the pressure activated device enables water from thesystem water inlet to be fed to the water delivery outlet when pressureat the inlet of the pressure adjusted device exceeds pressure of thepressure activated device outlet by an operating pressure of thepressure activated device.
 13. A system as claimed in claim 11,including a flow detector detecting a level of flow of water through thesystem, or including a flow detector in each water heater detecting arespective level of flow through each water heater, and a controllerresponsive to the flow detector or flow detectors to select a number ofheaters to be activated.
 14. A system as claimed in claim 11, includinga first temperature sensor sensing a temperature of water delivered tothe one or more water heaters via the hot water return pipe, and a pumpin the hot water return inlet being controlled by the first temperaturesensor, whereby the pump is turned on when the temperature sensed by thetemperature sensor falls below a first predetermined temperature. 15.The system as in claim 1, wherein the system water inlet is a mains coldwater source.
 16. The method as in claim 8, wherein the system waterinlet is a mains cold water source.
 17. The system as in claim 1,wherein the system water inlet is a mains cold water source.